Are you speaking about line follower robots?
Line follower robots follow the black or white line track. The basic components are a microcontroller, dc geared motors, motor driver IC L293D, batteries, IR-LED and IR photodiode pair as sensor. The following page has details on building a line follower robot:http://kmitl.ac.th/ kswichit/LFrobot/LFrobot.htm

we ourselves started from this page for building my own line follower in college.